The aim of this project is to elucidate the biochemical pathways through which gonadotropic hormones control the metabolism and steroidogenic responses of the interstitital cells of the testis. This includes the characterization of gonadotropin receptors for LH and FSH in the testis, and the analysis of the coupling mechanisms between receptor occupancy and androgen synthesis. The two major questions examined are: (1) the role of cyclic AMP and protein kinase in the initiation of the steroidogenic and trophic actions of gonadotrophin, and (2) the secondary sequence of events which leads to stimulation of the steroid biosynthetic pathway of the interstitial cell. This program has particular relevance to reproductive endocrinology, and is also aimed at a more general understanding of the mechanisms of action of peptide hormones upon target cells.